Process of separating vapors



`Fuly 29, 1941. H. R. LEGATsKl PROCESS OF SEPARA'IVING VAPQRS Filed Nov. l5, 1938 Patnted July A29, 1941 PROCESS F snranarmo varoas Harold R. Legatski, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation o! Delaware Application November 15, 1938, Serial No. 240,592

Claims.

This invention relates to the separation of val pors and gases from solutions and mixtures, and more particularly to a novel method for removing methane from high pressure. rich absorption oil.

In the usual oil absorption gasoline recovery system, the gas containing the hydrocarbon vapors is introduced into an absorber where it contacts an absorbent oil and the vapors become absorbed by said oil. The rich absorption oil is then passed through suitable distillation equipment for the separation of the absorbed hydrocarbons from the absorption oil. The portions distilled on' include gasoline and other vapors which may be condensed, and gases which may be permitted to escape or may be collected and used for heating or like purposes.

It is well known that methane is objection able in gasoline and in mixtures of hydrocarbon gases such as polymerization feed. Under the processes heretofore practiced, ithas been practically impossible to prevent the absorption and retention in the absorbent of a certain amount of methane. Further, in cracking and crackingpolymerization processes it is desirable to remove methane and hydrogen from the treated materials. The same applies to the removal of hydrogen sulilde or any other, undesirable tlxed gas or very volatile vapor from a solution or mixture of gas or vapors. Thus, a primary object of the present invention is to provide an improved process for removing a very volatile or "ilxed gas component from a solution or from a mixture of gases or vapors.

A further disadvantage of the absorption system heretofore in use is the loss of a considerable quantity of heavier gaseous hydrocarbons such as ethane, propane and butane although these hydrocarbons are of commercial value. Thus, a further object of the present invention is to provide an improved method for retaining ethane and heavier gases in the rich absorp tion oil for subsequent recovery.

A still further object of the present invention is to prepare a feed for polymerization in which the methane contained in the original hydrocarbon gases is removed.

The present invention contemplates the removal of methane from high pressure, rich ab-y sorption oil by countercurrently contacting saicb oil in a plurality of stages at successively lower pressures with vapors derived from said oil by decrease in pressure. Energy available in the high pressure oil and in dissolved methane which is to be discarded at a pressure less than absorber a rich gas inlet line pressure is used to compress said vapors and contact vapors and oil.

Thus additional objects of the present invention are the utilization of energy in the high pressure oil and waste methane and the promotion of the distillation oi' the rich oil which is due to the fact that while absorption is promoted by high pressure, distillation is promoted by low pressure.

Other objects and advantages will appear from the more detailed description of the invention following hereinafter, taken in conjunction with the accompanying drawing, which is a diagrammatic elevation of an apparatus suitable for carrying out the present invention.

In the drawing, I denotes an absorber having 2 near the bottom thereof. This gas, coming from any suitable source, is under considerable pressure either as a result of the natural pressure within the gas or induced therein by a compressor. The absorption medium is introduced into the absorber through a line 3 near the top oi' the absorber and comprises denuded oil from the still. o1' the high pressure oi' the gas, the absorption in absorber I is promoted to a high degree. The rich absorption oil under considerable pressure is run out of absorber i through a line 4 and passes through a jet 6 into a, vent tank 8 through an inlet l surrounding the jet 5. A vapor outlet 8 is provided at the upper end of the vent tank 6 for a purpose to be explained later.

Leaving the lower end of tank 8, through a line 9, the rich oil, at a slightly reduced pressure, is passed through a jet I0 into a second vent tank II through an inlet I2 surrounding the jet I0. A vapor line I3 extends from the upper end of tank II and is shown connected to the inlet 1 of tank 6 in such a way that the vapor or gas that is liberated in tank II as will later appear, is injected into theJ inlet 'l and will thereby aid the operation oi the jet Ii through which oil is injected into tank 6 from the absorber I.

The rich oil in tank II is run out through a line I4, through a jet I5 and into a third vent tank I 6 by way of an inlet Il surrounding the jet I5. The pressure in tank I6 is reduced from that in tank II. A vapor line I8 connects the upper end of tank I6 to inlet I2 of tank II in the same manner as line I 3 is yconnected to inlet 1.

'I'he rich oil from tank I6 is passed into a distillation unit`2I through pipe I9. The rich oil is subjected to heat in distillation unit 2| to denude the same. The evolved vapors are passed As a result through pipe for further processing to recover natural gasoline and kindred products. A line 2D connects inlet I1 to the pipe 25 similarly to the connections of the other vapor lines to their corresponding inlets, for returning vapors or gases from the distillation unit to the system.

passed through Batlies 24 are Denuded oil from the still may be pipe 22 to heat exchanger 23. shown in the vent tanks.

In explanation of the flow sheet described above, lrich oil from absorber I at pressure Pi, greater than. pressure P2 on vent tank 6, is used to inject vapors at inlet 1, which vapors are evolved in vent tank Il at a pressure P3 which is less than pressure P2. Simultaneous with and incidental to this operation is an intimate contacting of vapors from vent tank il and rich oil from absorber i in vent tank 6. Proceeding, rich oil from vent tank 6 at pressure P2, greater than pressure P3 on vent tank li is used to inject vapors at inlet I0, which vapors are evolved in vent tank I6 at pressure P4 which is less than pressure P3. This injecting operation involves an intimate contacting of vapor and oil in vent tank iisimilarly to the corresponding operation in vent tank 6. Proceeding further, rich oil from vent tank Il at pressure P3, greater than pressure P4 on vent tank I6 is used to inject vapors at inlet i5, which vapors are evolved in distillation unit 2l at pressure P5 which is less than pressure P4. This jetting operation provides an intimate contacting of vapor and oil in vent tank i5.

rThis type of operation, insofar as pressure reduction steps are concerned, depends only on the original pressure available and final pressure desired. The number of stages possible will be aiected by the volume of oil, volumes of vented vapor at any stage and the pressure drop available. it will he noted that both energy stored in high pressure oil and energy stored in dissolved gases in the oil are utilized in this process.

As can be seen from the drawing, the entire apparatus will amount to a pressure gradient iractionating device for removal or' methane from rich oil by solution or hydrocarbons heavier than methane in the. oil. The methane to be discarded Finally leaves the system at the highest vent pressure P2 from outlet pipe 8 in vent tank 3. Still vapors, which are methane free, enter the last venting stage, shown as vent tank iE, through vapor line 2G. Gil, methane free and at lov: pressure is removed from vent tank it and distilled in 2i to remove ethane and heavier absorbed hydrocarbons.

Though not apparent from the drawing, it will be seen that as the vapor progresses through this system, varying concentrations ci components will be encountered. These vapors, depending upon their economic value in commercial processes, may be removed at various stages without in any way having a deleterious effect upon the process.

The iiow sheet is intended to be diagrammatic only, in order that the essential parts of the process will stand out. Such items as valves and pressure and level controllers are known to the art and have therefore not been shown. However the unit may be constructed or controlled, the basic idea as here presented will remain the same.

Included in the possible operation of the process, is the addition of heat to the oil or vapor at any point in the process by heat exchangers such as those shown at 23, either for the purpose of increasing available energy from vented vapors or for the purpose of removing heat from lean oil leaving the still by heat exchange with rich oil going to the still.

It is readily apparent that the entire unit disclosed may be built into an existing plant without interfering with present heat exchange or distillation equipment. A low pressure plant may y at the distillation unit or in a later stage of the 'f liberated from said solution in subsegu -t process than the stage of methane removal; since methane is removed from the rich oil, it will be possible to condense the plant product at lower pressure and to conduct the oil distillation at a lower pressure and cost.

Modication and variations of the present disclosure will be apparent to those skilled in the art, and therefore I do not wish to be limited precisely to the construction herein shown except as may be required by the appended claims considered wtih reference to the prior art.

Having thus described the invention, what is claimed is:

1. The process of separating highly volatile vapors from a solution under high pressure coinprising contacting said solution in a plurality of stages at successively lower pressures with vapors liberated from said solution in subsequent stages and utilizing the pressure drop of said solution passing from stage to stage to move the vapors from stage to stage in the opposite direction.

2. The process of separating highly volatile vapors from a solution under high pressure comprising, contacting said solution in a plurality ci stages at successively lower pressures with vapors liberated from said solution in subsequentstages, and causing solution at higher pressure, passing from stage to stage, to inject vapors passing in the opposite direction from stage to stage.

3. The process of separatinrr highly voiatile vapors from a solution under high pressure ccinl prising, contacting said solution in pra tv of stages at successively lower pressure with vA causing solution at higher pressure, passing from stage to stage, to inject vapors passing in the opposite direction from stage to stage, and removing the most volatile vapor from the highest pressure stage.

4. The process of demethanizing high pressure, rich absorbent containing methane and higher boiling absorbed hydrocarbons and recovering said higher boiling hydrocarbons comprising, contacting said absorbent in a plurality of stages at successively lower pressures with vapors liberated from said absorbent in subsequent stages, causing absorbent at higher pressure, passing from stage to stage, to inject vapors passing in the opposite direction from stage to stage, removing methane from the highest pressure stage, and distilling rich absorbent free of methane to recover the higher boiling hydrocarbons from the absorbent.

5. The process of demethanizing high pressure,

rich absorption oil containing methane and higher boiling absorbed hydrocarbons and recovering said higher boiling hydroearbons comprising, contacting said oil in a plurality of stages at successively lower pressures with vapors liberated from said oil in subsequent stages, causing oil at higher pressure, passing from stage to stage, to inject vapors passing in the opposite direction from s lowestpressure stage.

stage to stage, removing methane from the highest pressure stage, dlstilling rich absorbent free of methane to recover the higher boiling hydrocarbons from the absorbent, and returning some of the vapors from the distillation step to the HARoLD R. LEGA'rsKr, 

